Electromagnetic actuating drives are required for opening and closing of the electrical contacts in an electromechanical switching device, such as a contactor or a relay. An electromagnet which has an armature and a yoke as closing elements represents a major part in actuating elements such as these. When a current flows through the coils of the electromagnet, then the resultant magnetic field accelerates the armature toward the yoke, until the pole faces of the armature and yoke rest on one another. When the current through the coils of the electromagnet is switched off, then the armature and yoke are opened again, generally by a mechanical resetting device, such as springs and the like. Moving contact pieces, which are connected to the armature, are moved with respect to stationary contact pieces in order to close and open the electrical contacts in an electromechanical switching device.
When the pole faces of the armature and yoke are resting on one another in the closed state, then adhesion forces are produced which prevent rapid opening. This has a disadvantageous effect on the switching times of the electromechanical switching device. For this reason, the pole faces of the closing elements of the electromagnet for an electromechanical switching device must have a certain roughness, which reduces the mutual adhesion between the pole faces. On the other hand, the pole faces must be flat since, otherwise, there would be an air gap between the closing elements, weakening the secondary flux in the magnet system. This leads to a reduction in the holding force and to an undesirable increase in the tendency of the switching device to hum.
In order to achieve the desired surface characteristics of the pole faces, it is already known for that surface of the closing element (which is normally in the form of a stamped part) which is intended to be used as the pole face to be treated by means of grinding disks. The surface character can be set by the choice of the grinding material applied to the grinding disks, for example corundum, and its granularity. One disadvantage is that a desirable narrow tolerance band cannot be achieved for the surface character.